126 MOLLUSCA FROM THE CRAG. 
Monracuta. Turton, 1822. 
LicuLa (sp.). Mont., 1808. 
Prrricoua (sp.). Gray, 1825. 
Erycrna (sp.). Desh., 1825: (sp.) Myst, 1844. 
MzsopesMa (sp.). Lovén, 1846. 
Generic Character. Shell equivalve, inequilateral, transversely oblong, or obliquely 
ovate, generally small and thin: surface smooth, or concentrically striated, and 
occasionally with a few radiating ridges. Hinge with two diverging elongated teeth, 
more conspicuous in one valve than in the other. Ligament internal, placed in a 
triangular fossette: impression by the mantle without a sinus. 
Animal oblong, having its mantle open in front; margins not fringed; without 
siphonal tubes (?) ; foot large and broad, furnished with a byssal groove. 
The name of this Genus was proposed in honour of Montague, the author of 
“Testacea Britannica;’ it is not, however, well determined, as two or three species, 
the animals of which have undergone a careful examination, so far as their diminutive 
forms will permit, seem to present considerable differences, and as far as regards the 
shells alone, or their dental characters, the species here included would probably justify 
their bemg separated into different Genera. As the authors of the ‘Hist. of Brit. 
Mollusca’ have made the same observation, and have not ventured to propose a new 
Genus where the animals present characters so materially different, it would ill 
become the Palzontologist with only the shells to guide him, to venture upon such 
a step. 
Shells apparently of this Genus, at least such as present similar dental characters, 
have been obtained from the Older Tertiaries of this country by Mr. Edwards; but 
nothing as yet known have been found in any Deposit of a more ancient date. Its 
Geographical range is at present limited to the European Seas and the Western Coast 
of America. 
1. MontTacuTA BIDENTATA, Montague. Tab. XII, fig. 17, a, 4. 
Mya pipentatTa. Mont. Test. Brit., p. 44, t. 26, fig. 5, 1803. 
— — Mat. and Rack. Linn. Trans., vol. viii, p. 41, 1807. 
— —_— Turt. Conch. Dict., p. 102, 1819. 
Monracuta BIDENTATA. Turt. Brit, Biv., p. 60, 1822. 
— — Gould. Iny. Massach., p. 59, 1841. 
-~ — Macgill. Moll. Aberd., p. 302, 1843. 
— — Thorpe. Brit. Mar. Conch., p, 52, fig. 58, 1844. 
— = Alder. Cat. Moll. North. and Durh., p. 95, 1846. 
— — Forb. and Hanl. Hist. Brit. Moll., vol. i, p. 75, pl. 18, figs 6, 
6a, 1849. 
ANATINA BIDENTATA. Brown. Illust. Brit. Conch., pl. 11, figs. 8, 9, 1827. 
